The technique of the present disclosure relates to a nickel-hydrogen storage battery.
Conventionally, a hydrogen-absorbing alloy has been used as a negative electrode material for a nickel-hydrogen storage battery. The hydrogen-absorbing alloy absorbs hydrogen during charging of the nickel-hydrogen storage battery and releases hydrogen during discharging of the nickel-hydrogen storage battery. The volume of the hydrogen-absorbing alloy expands or contracts in association with the absorption or the release of hydrogen. The hydrogen-absorbing alloy is pulverized as a result of the expansion and the contraction of the volume. The pulverization of the hydrogen-absorbing alloy brings about an increase in internal resistance of the nickel-hydrogen storage battery, and thereby the output of the nickel-hydrogen storage battery is reduced. An AB5 based alloy is mainly used as the hydrogen-absorbing alloy. An alloy containing cobalt is used among the AB5 based alloys for the purpose of suppressing the pulverization. A nickel-hydrogen storage battery in which the durability of the hydrogen-absorbing alloy is improved by suppressing the pulverization while the amount of expensive cobalt is reduced is disclosed in Japanese Laid-Open Patent Publication No. 2008-166027.
However, since the expansion and contraction of the hydrogen-absorbing alloy during charging and discharging of the nickel-hydrogen storage battery are unavoidable, the pulverization of the hydrogen-absorbing alloy is unavoidable. Moreover, when the ratio of the theoretical capacity of the negative electrode to the theoretical capacity of the positive electrode is made small in order to improve the weight energy density, the load of the negative electrode is increased and thereby the pulverization of the hydrogen-absorbing alloy is accelerated. Therefore, it is desired to suppress the increase in the internal resistance of the nickel-hydrogen storage battery attributable to the pulverization of the hydrogen-absorbing alloy.